The present invention relates to polyurethane polymers. More particularly, the present invention relates to polyurethane foams having reduced visible emissions during processing, as well as improved physical properties.
Flexible polyurethane foams are commonly prepared for a variety of commercial uses. Such uses include packaging, insulation, cushioning, carpet underlay and the like. For these purposes it is desirable for the foams to exhibit good load bearing capability, resiliency, tensile strength and tear strength, in order to meet acceptable performance and durability standards. Flexible polyurethane foams may be produced by either slab foam or molded processes. Slab foams are produced in large buns which, after curing, are sliced or otherwise formed into useful shapes. For example, carpet underlay can be prepared in this manner. In contrast, molding is used to directly produce foam objects in essentially their final shape and form. Automotive seating and some furniture cushioning are commonly molded.
Currently flexible polyurethane foams are most often prepared by the well-known "one-shot" technique, in which the starting materials are reacted and foamed in one step. The starting materials usually include a polyol, a polyisocyanate, one or more catalysts and surfactants and, as a blowing agent, water. Auxiliary blowing agents such as highly volatile halocarbon compounds are also frequently used.
One commonly used component of many polyurethane foams is one or more antioxidants. Antioxidants are generally defined to mean any material added to a foam formulation to improve the resistance of the foam to oxidative type reactions. Such reactions, occurring mainly during the cure and cooling phase of processing due to the exothermic nature of the foam-forming reaction, tend to result in discoloration of the foam, also called "scorch". Because this discoloration reduces the commercial acceptability of the final product, one or more antioxidants is generally employed in most formulations. Antioxidants also play a part in reducing discoloration over time, often exhibited as a "yellowing" of the foam, and in maintaining physical properties that are lost due to the general degradation of the foam during the curing period or during ageing.
However, a particular problem encountered in polyurethane foam processing is the generation of visible emissions, particularly during mechanical cooling. These emissions, often in the form of a white or gray "smoke", are most frequently seen when certain antioxidants are used in preparation of the foam, but may also occur under other circumstances, when certain types of other materials are included in formation of the foam. Because such emissions frequently result in violation of air quality regulations and standards with resultant penalties, a means of eliminating or reducing the visible emissions, while at the same time maintaining foam physical properties and overall quality, is needed in the art.